Sorry to insist, but referring back to my post "how: subordinating conjunction (2)" could you tell me how you differentiate :a) "how" as an adverb from a subordinating conjunction ? b) an nominal clause from an adverbial clause ?I'm lost.

Look at this example, where the adverb 'how' functions conjunctively (i.e.introducing a subordinate clause):

I don't know HOW he did it.

The subordinate clause (underlined) serves nominally, here as object of the verb. It is like saying I don't know this/that. The word 'how' itself here means simply 'in what way' - i.e. the normal, basic meaning of 'how' as an interrogative.

Now look at this example, in which 'how' serves as a true subordinating conjunction (as noted previously, however, suitable for informal use only).

Do it HOW you did it last time.

The clause that it introduces is adverbial. It is like saying '...in this way/in that way'.

Now note that, unlike the first example, 'how' in the second could not be rephrased as 'in what/which way', but represents a more complex structure: 'in the way in which'.

I think I get it now. 1) Does an adverb introduce a nominal clause (functioning as an object) and a subordinating conjunction introduce an adverbial clause (functioning as an adjunct/adverbial of time/manner...)?

2) Does a clause introduced by a conjunctive adverb answer the question "what" and a clause introduced by a subordinator answer the question "in what way" ?

e.g. "I don't know how he can do it" answers the question "what is it that I don't know?"Would it be the same for "I don't know when they are leaving/ why they are leaving"?

However, I still have some doubts about this sentence:If you say: "Do it HOW you did it last time", it means "Do it THE WAY you did it last time", right?Isn't it the same as: "This is HOW the accident happened / This is HOW I make a vegetable soup" = "This is THE WAY the accident happened / I make a vegetable soup"?

Or is it possible that linking verbs such as "to be" can never (?) be followed/modified by an adverbial of manner ?

I'm very much afraid that the supplemental questions you have posed here indicate clearly that you have understood rather less well than you think. I therefore don't believe that there would be much point in my giving detailed answers to these questions, when they would be likely only to breed more of the same.

I think that, before posting any further questions on technical grammatical distinctions, you really need to go away and carefully study several introductions to English grammar, aiming to acquire a sound basic knowledge of the meanings of all the relevant terms. Only then will there be any real value in asking whether a certain word is an adverb or a conjunction.

I am also forced to wonder what motivates you to post such questions as you do: if you are aiming to teach grammar, then you clearly need to gain a much better grasp of it yourself before doing so. If, on the other hand, you are a student of grammar, then questions such as those you pose would surely be better addressed to your teacher/tutor.

I trust that you will not take offence at these suggestions, but rather take them in the constructive spirit in which they are offered.